Virtual tape device and method for selecting physical tape

Abstract

A virtual tape device being located between a host and a tape library and storing data as a virtual logical volume in a storage, has a calculator that calculates a time period in which a robot moves, from a cell to a drive device, the physical tape in accordance with an instruction when the instruction is issued to recall the target logical volume redundantly stored on the physical tapes stored in two or more cells included in different tape libraries or in the same tape library and to store the target logical volume, a calculator that calculates a time period for tape positioning, and a unit that calculates a time period on the basis of the time period in which the robot moves from the cell to the drive device and the time period for the tape positioning, and that selects a physical tape corresponding to the shortest time period.

1 . A virtual tape device that is located between a host device and a tape library device and stores, as a virtual logical volume in a large scale storage device, data that has been transmitted and is to be received between the host device and the tape library device, the virtual tape device comprising:
 a robot movement time period calculator that calculates, for each of physical tapes on which a target logical volume to be recalled exists, a time period in which a robot moves, from a cell to a drive device, the physical tape on which the target logical volume is to be stored in accordance with a recall instruction when the recall instruction is issued to recall the target logical volume redundantly stored on the physical tapes stored in two or more cells included in different tape library devices or in the same tape library device and to store the target logical volume in the large scale storage device;   a tape positioning time period calculator that calculates, for each of the physical tapes on which the target logical volume exists, a time period for tape positioning that is performed to read the target logical volume from the physical tape; and   a physical tape selecting and determining unit that calculates, for each of the physical tapes on which the target logical volume exists, a time period from the time when the recall instruction is issued to the time when the target logical volume starts to be read from the physical tape, on the basis of the time period in which the robot moves from the cell to the drive device and the time period for the tape positioning, and that selects, from among the physical tapes as a physical tape to be subjected to a recall process to be performed in accordance with the recall instruction, a physical tape that corresponds to the shortest time period from the time when the recall instruction is issued to the time when the target logical volume starts to be read from the physical tape.   
     
     
         2 . The virtual tape device according to  claim 1 ,
 wherein the robot movement time period calculator calculates, for each of the physical tapes on which the target logical volume exists, the time period in which the robot moves the physical tape from the cell to the drive device, on the basis of information on the position of the robot located when the recall instruction is issued, information on the position of the cell in which the physical tape on which the target logical volume exists is stored, and information on the position of the drive device in which the physical tape on which the target logical volume exists is mounted.   
     
     
         3 . The virtual tape device according to  claim 1 ,
 wherein when the recall instruction is issued, the tape positioning time period calculator references a logical-physical correspondence relationship information database storing correspondence relationships between logical volumes stored in the large-scale storage device and physical volumes stored on the physical tapes and acquires, for each of the physical tapes on which the target logical volume exists, information on the position of a region in which a data block of the target logical volume is stored on the physical tape on which the target logical volume exists, and the tape positioning time period calculator calculates, for each of the physical tapes on which the target logical volume exists, the time period for the tape positioning on the basis of the acquired information on the position of the region.   
     
     
         4 . The virtual tape device according to  claim 1 , further comprising an error determining unit that determines, for each of the physical tapes on which the target logical volume exists, an error occurrence in the physical tape when the recall instruction is issued,
 wherein the physical tape selecting and determining unit determines, for each of the physical tapes on which the target logical volume exists, whether or not the physical tape on which the target logical volume exists is selectable as the physical tape to be subjected to the recall process.   
     
     
         5 . The virtual tape device according to  claim 4 , further comprising an error retry number table storage unit that stores information on occurrences of various types of error retries that are performed on all physical tapes installed in the tape library devices,
 wherein when the recall instruction is issued, the error determining unit determines, for each of the physical tapes on which the target logical volume exists, an error occurrence in the physical tape by acquiring, from the error retry number table storage unit, information on occurrences of the various types of error retries performed on the physical tape.   
     
     
         6 . A method for selecting a physical tape by a virtual tape device that is located between a host device and a tape library device and stores, as a virtual logical volume in a large-scale storage device, data that has been transmitted and is to be received between the host device and the tape library device, the method comprising:
 calculating, for each of physical tapes on which a target logical volume to be recalled exists, a time period in which a robot moves, from a cell to a drive device, the physical tape on which the target logical volume is to be stored in accordance with a recall instruction when the recall instruction is issued to recall the target logical volume redundantly stored on the physical tapes stored in two or more cells included in different tape library devices or in the same tape library device and to store the target logical volume in the large-scale storage device;   calculating, for each of the physical tapes on which the target logical volume exists, a time period for tape positioning that is performed to read the target logical volume from the physical tape; and   calculating, for each of the physical tapes on which the target logical volume exists, a time period from the time when the recall instruction is issued to the time when the target logical volume starts to be read from the physical tape, on the basis of the time period in which the robot moves the physical tape from the cell to the drive device and the time period for the tape positioning, and selecting, from among the physical tapes as a physical tape to be subjected to a recall process to be performed in accordance with the recall instruction, a physical tape that corresponds to the shortest time period from the time when the recall instruction is issued to the time when the target logical volume starts to be read from the physical tape.   
     
     
         7 . The method according to  claim 6 ,
 wherein the time period in which the robot moves the physical tape from the cell to the drive device is calculated for each of the physical tapes on which the target logical volume exists on the basis of information on the position of the robot located when the recall instruction is issued, information on the position of the cell in which the physical tape on which the target logical volume exists is stored, and information on the position of the drive device in which the physical tape on which the target logical volume exists is mounted.   
     
     
         8 . The method according to  claim 6 ,
 wherein when the recall instruction is issued, the time period for the tape positioning is calculated for each of the physical tapes on which the target logical volume exists on the basis of information on the position of a region in which a data block of the target logical volume is stored on the physical tape.   
     
     
         9 . The method according to  claim 6 , further comprising:
 determining, for each of the physical tapes on which the target logical volume exists, an error occurrence in the physical tape when the recall instruction is issued; and   determining, for each of the physical tapes on which the target logical volume exists, whether or not the physical tape on which the target logical volume exists is selectable as the physical tape to be subjected to the recall process.   
     
     
         10 . The method according to  claim 6 , further comprising:
 storing information on occurrences of various types of retries that are performed on all physical tapes installed in the tape library devices; and   determining, for each of the physical tapes on which the target logical volume exists, an error occurrence in the physical tape by acquiring, from an error retry number table, information on occurrences of the various types of retries performed on the physical tape, when the recall instruction is issued.